1. Field of the Invention
The present invention relates to cationic pigments and aqueous compositions containing the same and, more particularly, to ink compositions useful for imaging applications, such as ink jet ink compositions.
2. Discussion of the Related Art
Aqueous systems are increasingly being used in many applications such as automotive and industrial coatings, paints, papers, inks, toners, adhesives, latexes, etc. as manufacturers face increased pressure to replace conventional solvent based systems. Such aqueous systems are known and generally contain a colorant, such as a dye, which is soluble in the aqueous vehicle, such as water or a mixture of water and a water-soluble or water-miscible organic solvent.
Although dye-based compositions are readily utilized, dyes have several disadvantages when used in aqueous ink systems. For example, dyes, being water-soluble in a water/organic mixture, may dissolve and run when exposed to moisture or water. Dye images may further smear or rub-off on contact with felt pen markers or upon being rubbed or touched by a finger. Dyes also exhibit poor light stability when exposed to visible or ultraviolet light.
Pigments are also known as colorants in aqueous compositions but have not received a wide degree of acceptance in aqueous systems, such as ink jet inks, because of problems associated with the performance and reliability of the composition, i.e., print properties, stability, latency, and the like. Examples of such pigments include carbon black, titanium dioxide white, cobalt blue (CoO--Al.sub.2 O.sub.3), phthalocyanine blue, phthalocyanine green, and chrome yellow (PbCrO.sub.4).
U. S. Pat. Nos. 5,571,311; 5,630,868; 5,707,432; 5,803,959; and 5,837,045 and PCT Publication No. WO 96/18688; and PCT Publication No. WO 96/18695 (all incorporated in their entirety herein by reference), describe novel surface-modified pigments and aqueous compositions containing such surface-modified pigments. Although such surface-modified pigments are a considerable improvement over dye-based or traditional pigment systems (i.e. pigments requiring stabilization with a polymer or surfactant compositions), a continuing need exists for improved cationic based pigments, as well as aqueous or solvent based compositions containing such pigments, especially for use in ink compositions which require long term colloidal stability and lightfastness. It is also desirable to produce improved aqueous ink compositions which exhibit improved recoverability in their respective printing systems while providing good print properties. A further need exists for improved aqueous ink compositions which generate print images having improved waterfastness.